I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
Cheers, Max
On 2 August 2013 15:08, Max Leske maxleske@gmail.com wrote:
I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
err.. i see dict add: but where dict was declared?
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
Cheers, Max
Hi Max and Igor,
First Igor, I'm sure Max meant collection and not dict, probably just a typo caused by playing around.
Max, this is not a bug (other than in your test),
collection add: [ methodScope ] doesn't (and shouldn't) add a block with the value of methodScope at the time of the add: but adds a block with (for lack of a better term) a pointer to the methodScope variable. When the block is executed (sent #value) the value of the block is the current value of methodScope, in your case 2. Try this:
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. collection add: [ methodScope ] ]. methodScope := 5. collection do: [ :block | Transcript show: block value; cr ]
Lou
On 2 August 2013 15:08, Max Leske maxleske@gmail.com wrote:
I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
err.. i see dict add: but where dict was declared?
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
Cheers, Max
----------------------------------------------------------- Louis LaBrunda Keystone Software Corp. SkypeMe callto://PhotonDemon mailto:Lou@Keystone-Software.com http://www.Keystone-Software.com
On 2 August 2013 14:08, Max Leske maxleske@gmail.com wrote:
I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
"dict" should be "collection".
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
While weird, it looks right. Each iteration you store the index in methodScope. In the collection you store a block that deferences methodScope. After the second iteration, methodScope = 2, so in both blocks, the derefence yields 2.
frank
Cheers, Max
On 2 August 2013 15:15, Frank Shearar frank.shearar@gmail.com wrote:
On 2 August 2013 14:08, Max Leske maxleske@gmail.com wrote:
I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
"dict" should be "collection".
Max, can you rewrite the code sample, because this line:
dict add: [ methodScope ]
adding closure to collection? or should it be:
dict add: [ methodScope ] value ?
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
While weird, it looks right. Each iteration you store the index in methodScope. In the collection you store a block that deferences methodScope. After the second iteration, methodScope = 2, so in both blocks, the derefence yields 2.
frank
Cheers, Max
This is not a bug.
Here your variable methodScope is defined outside the block, therefore all the blocks and the method refers to the same variable when calling methodScope.
Your code is the same as if you wrote : | methodScope | methodScope := 1. methodScope := 2. At the end, methodScope is of course 2.
If you want the result : 1 2 you have to declare the variable in the block (then there are different variable named methodScope, actually 1 per activation of the block.
collection := OrderedCollection new. 1 to: 2 do: [ :index | | methodScope | methodScope := index. dict add: [ methodScope ] ]. collection do: [ :block | Transcript show: block value; cr ]
2013/8/2 Max Leske maxleske@gmail.com
I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
Cheers, Max
Sorry, yes, "dict" should be "collection".
On 02.08.2013, at 15:16, Clément Béra bera.clement@gmail.com wrote:
This is not a bug.
Here your variable methodScope is defined outside the block, therefore all the blocks and the method refers to the same variable when calling methodScope.
Yes, I understand that. I just wanted to make sure that's the intended functionality. The reason I ask is that the error isn't easy to spot and there's no cue that one might be doing something wrong (It's not my code by the way :P). Especially for newcomers this can be a tricky one.
I totally agree with you that the variables belong to the block and should be declared there.
Your code is the same as if you wrote : | methodScope | methodScope := 1. methodScope := 2. At the end, methodScope is of course 2.
If you want the result : 1 2 you have to declare the variable in the block (then there are different variable named methodScope, actually 1 per activation of the block.
collection := OrderedCollection new. 1 to: 2 do: [ :index | | methodScope | methodScope := index. dict add: [ methodScope ] ]. collection do: [ :block | Transcript show: block value; cr ]
2013/8/2 Max Leske maxleske@gmail.com
I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
Cheers, Max
On 2 August 2013 15:27, Max Leske maxleske@gmail.com wrote:
Sorry, yes, "dict" should be "collection".
On 02.08.2013, at 15:16, Clément Béra bera.clement@gmail.com wrote:
This is not a bug.
yes, the expression:
[ methodScope ]
does not capturing the current value of methodScope variable.
means that closure, when evaluated will always return the value methodScope at the moment of evaluation.
Closures do not capturing values of free variables, because then it will mean different semantic than rest of code (in method's body).
Here your variable methodScope is defined outside the block, therefore all the blocks and the method refers to the same variable when calling methodScope.
Yes, I understand that. I just wanted to make sure that's the intended functionality. The reason I ask is that the error isn't easy to spot and there's no cue that one might be doing something wrong (It's not my code by the way :P). Especially for newcomers this can be a tricky one.
I totally agree with you that the variables belong to the block and should be declared there.
Your code is the same as if you wrote : | methodScope | methodScope := 1. methodScope := 2. At the end, methodScope is of course 2.
If you want the result : 1 2 you have to declare the variable in the block (then there are different variable named methodScope, actually 1 per activation of the block.
collection := OrderedCollection new. 1 to: 2 do: [ :index | | methodScope | methodScope := index. dict add: [ methodScope ] ]. collection do: [ :block | Transcript show: block value; cr ]
2013/8/2 Max Leske maxleske@gmail.com
I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
Cheers, Max
On 02.08.2013, at 15:35, Igor Stasenko siguctua@gmail.com wrote:
On 2 August 2013 15:27, Max Leske maxleske@gmail.com wrote:
Sorry, yes, "dict" should be "collection".
On 02.08.2013, at 15:16, Clément Béra bera.clement@gmail.com wrote:
This is not a bug.
yes, the expression:
[ methodScope ]
does not capturing the current value of methodScope variable.
means that closure, when evaluated will always return the value methodScope at the moment of evaluation.
Closures do not capturing values of free variables, because then it will mean different semantic than rest of code (in method's body).
Ok, thanks.
Here your variable methodScope is defined outside the block, therefore all the blocks and the method refers to the same variable when calling methodScope.
Yes, I understand that. I just wanted to make sure that's the intended functionality. The reason I ask is that the error isn't easy to spot and there's no cue that one might be doing something wrong (It's not my code by the way :P). Especially for newcomers this can be a tricky one.
I totally agree with you that the variables belong to the block and should be declared there.
Your code is the same as if you wrote : | methodScope | methodScope := 1. methodScope := 2. At the end, methodScope is of course 2.
If you want the result : 1 2 you have to declare the variable in the block (then there are different variable named methodScope, actually 1 per activation of the block.
collection := OrderedCollection new. 1 to: 2 do: [ :index | | methodScope | methodScope := index. dict add: [ methodScope ] ]. collection do: [ :block | Transcript show: block value; cr ]
2013/8/2 Max Leske maxleske@gmail.com
I just came across this (possible) bug and I'm able to reproduce it in Pharo 2.0 and 3.0 with the latest PharoVM (found in a 1.3 with NBCog):
expected (by my feeble mind): 1 2
actual: 2 2
| methodScope | collection := OrderedCollection new. 1 to: 2 do: [ :index | methodScope := index. dict add: [ methodScope ] ].
collection do: [ :block | Transcript show: block value; cr ]
I'm aware that using method temps in this way is not good programming style (usually) but I still think this behavior is curious if not at least very likely to cause a lot of weird errors.
Should I open a bug report?
Cheers, Max
-- Best regards, Igor Stasenko.
vm-dev@lists.squeakfoundation.org
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Clément Béra -
Frank Shearar -
Igor Stasenko -
Louis LaBrunda -
Max Leske